1. Field of the Invention
The invention relates to a steel with composite plating film having a metal plated layer containing photocatalyst particles with a semiconductor material formed on the surface, and a manufacturing method thereof. Further, the present invention relates to corrosion resistant film for a metal used in the dark with not illuminated, a method of preventing corrosion of metal in the dark and a composite film.
2. Related Art Statement
Although steel materials are widely used for structures, it is susceptible to rust when subjected to severe corrosive conditions. It is thus needed to perform corrosion resistant treatment. Plating is representative as the corrosion resistant treatment, and zinc plating has been most widely used.
The mechanism of the method of electrochemical corrosion prevention of the zinc plating will be described. The ionization tendency of fixed zinc is larger than that of steel. In the case that galvanized steel and electrolyte contact each other, zinc is dissolved earlier and electrons are injected into the steel. The immersion potential of a steel is rapidly shifted to “less noble potential” to realize the cathodic protection of the steel. The immersion potential of a steel under the effect of sacrificial corrosion prevention represented with respect to a saturated silver chloride electrode corresponds with a value of minus 730 mV or lower (vs. Ag/AgCl). Zinc plating is described in, for example, “Corrosion Science and Engineering”.
It has disclosed photo-electrochemical cathodic protection utilizing titanium oxide as a photocatalyst (Japanese patent publication Nos. 2001-247985A, 2001-262379A, 2002-69677A and 2002-273238A).
Further, it is disclosed to provide a metal plating layer containing photocatalyst particles in Japanese Patent publication Nos. 2000-84415A and 2005-58900A.
Further, the provision of a photocatalyst layer on a plated layer is described in the following documents.
Japanese patent publication No. 2000-61193A
Japanese patent publication No. 2005-168784A
Japanese patent publication No. H11-276891A
Japanese patent publication No. 2002-254556A
Japanese patent publication No. 2000-282260A
Japanese patent publication No. 2000-178783A
Japanese patent publication No. 2005-139532A
Further, the inventors have disclosed a corrosion prevention paint for metal, containing a sacrificial anode metal and an photocatalyst in Japanese patent publication No. 2006-143815A.
Although a metal, particularly carbon steel, is an excellent material for a structure, it had a defect of deterioration due to rust. The method of corrosion prevention of carbon steel is mainly categorized into two kinds of methods; physical and electrochemical corrosion prevention. A physical corrosion prevention is a method of covering the surface of a steel with a chemically inert film to prevent oxygen and water of the environment inducing the corrosion. Representatives are chrome plating, phosphating, chemical passivation treatment and anti-corrosion steel. Further, although it is not a chemical treatment, a protective coating is obtained by covering the surface of a steel with an organic paint such as epoxy, polyurethane resin or the like and has the effect of preventing water or chloride ions. It is one of a measure of preventing corrosion of a steel by an organic paint.
However, according to these physical corrosion prevention methods, damages or peeling may be generated in the corrosion prevention films due to various reasons. And water or oxygen penetrates into the metal surface through defects and cracks. Severe corrosion starts from there.
On the other hand, the method of electrochemical corrosion prevention is covering the surface of a steel with a metal plating so that the plated metal functions as an anode to prevent corrosion of the underlying steel electrochemically. This is so-called cathodic protection. Representatives are tinning, zinc plating or the like carried out in factories. Further, zinc dust anticorrosive paint (zinc-rich paint) coating containing zinc metal particles, the representative of cathode corrosion prevention, is used widespread on sites. Zinc-rich paint is described in, for example, Japanese patent publication No. H07-133442A.